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    A Tutorial on Nonorthogonal Multiple Access for 5G and Beyond
    (Wiley-Hindawi, 2018) Aldababsa, Mahmoud; Toka, Mesut; Gokceli, Selahattin; Kurt, Gunes Karabulut; Kucur, Oguz
    Today's wireless networks allocate radio resources to users based on the orthogonal multiple access (OMA) principle. However, as the number of users increases, OMA based approaches may not meet the stringent emerging requirements including very high spectral efficiency, very low latency, and massive device connectivity. Nonorthogonal multiple access (NOMA) principle emerges as a solution to improve the spectral efficiency while allowing some degree of multiple access interference at receivers. In this tutorial style paper, we target providing a unified model for NOMA, including uplink and downlink transmissions, along with the extensions to multiple input multiple output and cooperative communication scenarios. Through numerical examples, we compare the performances of OMA and NOMA networks. Implementation aspects and open issues are also detailed.
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    Performance analyses of TAS/Alamouti-MRC NOMA in dual-hop full-duplex AF relaying networks
    (Wiley, 2023) Toka, Mesut; Guven, Eray; Durmaz, Mehmet Akif; Kurt, Gunes Karabulut; Kucur, Oguz
    In this article, performance of a multi-user downlink non-orthogonal multiple access system in dual-hop full-duplex amplify-and-forward relaying networks is investigated over Nakagami-m fading channels in the presence of channel estimation error and feedback delay. The base station applies transmit antenna selection (TAS)/Alamouti space-time block coding scheme, while the users exploit maximum-ratio combining to utilize benefits of receive diversity. To demonstrate superiority of the proposed system, outage probability (OP) is inves-tigated, and tight lower bound expression is derived to support the exact OP. Moreover, asymptotic analyzes are also conducted for ideal and practical condi-tions to provide further insights into the OP in high signal-to-noise ratio region. In addition, software defined radio based test-bed implementation is realized to confirm the analysis and show feasibility of the proposed system. Theoreti-cal analyzes verified by simulations and practical implementations demonstrate that more performance improvement can be achieved for the weakest user (with the lowest channel gain) in the case of practical conditions when compared to ideal cases. Also, both diversity order and array gain are dominant in achieving minimum OP (based on relay location) in ideal conditions, while only array gain has effect in practical manner.